Borehole Seismic Networks and Arrays

Abstract

Borehole strings and chains; Buried grids; Downhole networks and arrays; Vertical arrays; VSP DefinitionIn the broadest sense, borehole networks and arrays are assemblies of geophysical instruments placed in the subsurface via boreholes. This article focuses on their seismological applications. While common usage often blurs the distinction between a network and an array, this article explicitly distinguishes between their operational theories and engineering practices, and in the case histories and examples provided. To strictly qualify as an array, the assembly of instruments must include matching or similar sensors located at different depths in one well or lateral separated in different wells. The combined natural-frequency responses and spacing of the sensors must also include a range over which they can be used to improve signal detection and analysis via time series processing. Outside of this range a borehole assembly acts as a network of independent detectors. Early DevelopmentsThe general use of boreholes for making subsurface seismic measurements appears to have begun nearly 100 years ago. McCollum and LaRue (1931) report that "during the past year